Although many spark ignition internal combustion engines now have essentially fixed initial ignition timing by using a crankshaft position sensor or the like, a large number of such engines still rely upon an ignition timing system wherein a rotor rotates within a distributor to distribute the spark impulse to the individual cylinders as the rotor revolves within the distributor. Such systems are mandatory in certain classes of racing vehicles. This basic principle is the same for mechanical points-type distributors in which a cam lobe(s) on the distributor shaft periodically opens and closes the breaker points, and for so-called “breakerless” systems in which magnetism or light (visible or invisible spectrum) is used as the timing signal. The same basic timing principle is used with magneto ignition systems. The primary difference between the conventional distributor system and the magneto system is that the magneto also serves as an electrical generator to produce the electrical energy required for the ignition system.
Basic distributor and magneto ignition systems universally rely upon a distributor shaft that is geared to a rotary component of the engine, generally a camshaft or crankshaft. The distributor rotor is affixed to the end of the distributor shaft within the distributor housing. Due to the tolerances and gear lash inherent in such a mechanical system, as well as point wear in a mechanical point system, the distributor or magneto is always provided with some means for adjusting the timing of the ignition pulse to each cylinder. This is generally accomplished by allowing the distributor or magneto to be rotated slightly in its installation and locked into place when the timing has been set accurately. In the case of a magneto ignition system, this is known as “external timing,” as opposed to internal magneto timing in which the timing of the rotary components for maximum efficiency in generating the required electrical energy (“e-gap”) is accomplished.
There are essentially two methods of setting the ignition timing with such an ignition system: The timing may be set with the engine operating (running), or with the engine stationary (shut down). In the case of an operating engine, the gear lash and play in the system is automatically taken up due to engine rotation driving the distributor or magneto. The mechanic may set the timing by using a timing light temporarily connected to the ignition lead to the designated number one cylinder, rotating the distributor or magneto to set the timing as required, and securing the distributor or magneto in place by means of the conventional clamp or other means provided.
However, in the case of a stationary engine, the mechanic must take into account any play and gear lash in the distributor or magneto drive system. This is particularly true in situations where the distributor or magneto has been removed from the engine, e.g., for engine rebuild or other major work, ignition system overhaul or replacement, etc. In such cases, the mechanic turns the engine over to position the timing marks so that the number one piston is at or near top dead center on its compression stroke, and adjusts the distributor or magneto to an initial position that appears to be at least close to the desired ideal timing. However, the mechanic must still set the timing using a timing light or audible signal, the timing light or signal being activated when the points (or other electromagnetic signal) first open. This method of timing using a timing light when the engine is stationary will still not provide the required degree of accuracy due to the gear lash and play in the distributor drive system. A knowledgeable mechanic will always turn the engine slightly in a direction opposite its normal direction of rotation, and then rotate the engine in the operating direction to the desired external timing mark on the crankshaft pulley or damper in order to remove gear lash and play when setting timing on a stationary engine. Checking timing after this procedure may reveal that the timing is still not optimal, and the process must be repeated while the engine is operating. Obviously, this is a tedious and time-consuming task.
Thus, an internal combustion engine ignition timing tool solving the aforementioned problems is desired.